The present invention generally relates to a wireless communication system, and more particularly to methods and apparatus for determining a direction of arrival (DOA) of a signal transmitted by a remote unit in a wireless communication system.
There are numerous applications that can use the location of a subscriber unit in a wireless communication system. For example, the location of the subscriber unit can be used for emergency services, so that police, fire and/or medical services can be dispatched to the location of the subscriber requesting such an emergency service. In addition, location of the subscriber unit can be used in detecting fraudulent use of the communication system, police investigations, and the like. Furthermore, the location of a subscriber unit can be used to improve performance of the wireless communication system. For example, wireless communication systems that utilize beam-forming transceivers can tune the beams based at least in part on the direction of arrival (DOA) of a signal from the subscriber unit.
Wireless communication systems currently have the capability for determining the location of a subscriber unit. For example, a subscriber unit can be located within a cell through identification of the base station antenna used to provide service in the cell. However, as a cell can have a one to three mile radius, the location of the subscriber unit is relatively imprecise and impractical for most applications. Additional systems have been proposed and implemented for determining the location of a subscriber unit, such as the use of a Global Positioning System (GPS) unit at the subscriber unit, triangulation onto a transmitting subscriber unit, and Amplitude Difference-based Angle Of Arrival Estimation (AD-AOA) as described in U.S. Pat. No. 5,786,791, issued to Eugene J. Bruckert on Jul. 29, 1998 and assigned to Motorola, Inc., which is hereby incorporated by reference.
The AD-AOA estimation provides an accurate location of a subscriber unit in a wireless communication system, accounts for multi-path scattering of a received signal and unequal receiver gains. The AD-AOA estimation is preferably implemented with a phased antenna array having antenna elements that are spaced at a distance that is less than one-half of a wavelength of the carrier frequency of the received signal. However, the AD-AOA estimation and other location identification techniques and apparatus are preferably implemented with any number of phased antenna array configurations, including a configuration of a phased antenna array having antenna elements that are spaced at a distance that is greater than one-half of a wavelength of the carrier frequency of the received signal.
In view of the foregoing, is should be appreciated that it would be desirable to provide methods and apparatus for determining a DOA of a subscriber unit in a communication system. In addition, it should be appreciated that it would be desirable to provide methods and apparatus for determining a DOA of a subscriber unit in a communication system with any number of phased antenna array configurations, including a configuration of a phased antenna array having antenna elements that are spaced at a distance that is greater than one-half of a wavelength of the carrier frequency of the received signal. Furthermore, additional desirable features will become apparent to one skilled in the art from the following detailed description of the drawings and appended claims.